1. Field of the Invention
This invention relates to a method and apparatus for manufacturing a transparent conductive substrate for a large size display panel.
2. Description of the Prior Art
Recently intensive efforts have been concentrated on development of large size, high precision display panels of either light reception (passive) type or light emission (active) type, such as liquid crystal display (LCD), electroluminescence (EL), electrochromic display (ECD), electrophoretic display, and plasma display panel (PDP).
Above all, in an example of large capacity display panel to display a number of characters and images, upper and lower electrodes at both sides of a display medium are arranged in a X-Y matrix as shown in FIG. 15, and, for example, to display a monochromatic image of 1,000.times.1,000 pixels, 1,000 fine strip electrode films are required for each of X side and Y side. Usually, the electrode films of one side must be transparent conductive films in order to observe the display.
On the other hand, in the case of the display panel structure as shown in FIG. 15, regardless whether the display method is LCD, LE, ECD or PDP, it is called "a simple matrix panel structure".
To produce a simple matrix panel of large display capacity, as shown in FIG. 15, a technology to form the multiple fine strip transparent conductive films uniformly at high yield is indispensable. A conventional manufacturing method of transparent conductive substrates comprises, as shown on page 156 of The Latest Technology of Liquid Crystals by Shoichi Matsumoto et al. (first published 1983 by Kogyo Chosa Kai), the steps of forming a transparent conductive layer of indium oxide (In.sub.2 O.sub.3), tin oxide (SnO.sub.2) or others on a stationary or rotating transparent substrate of glass or plastics over nearly the entire surface by means of sputtering, vacuum deposition or other processes, taking out the substrate from a vacuum environment, and patterning the electrodes in desired shapes on the transparent substrate by photo etching process. In this method, electrode forming and patterning are separated from each other. In a special case, electrodes may be deposited while the substrate is covered with a metallic mask patterned in a specified shape, which is called "mask evaporation method". In this case, electrode forming and patterning can be effected simultaneously, but in the case of forming a large size substrate, tight contact of mask and substrate becomes difficult, and it may be hard to form electrode films of uniform thickness on a large area of substrate. In the case of the above photo etching process, high precision patterning is barely possible on a substrate of up to 30 cm square, but on a meterwide substrate, uniform application of photo resist, uniform exposure, and production of large size high precision photo mask are technically difficult, whereas in the case of the mask evaporation process, difficulties are found in the contact between the large substrate and mask, mechanism of replacement of high precision masks, and mass producibility. Thus, manufacture of the meter-wide transparent conductive substrate of flat display panel is an undeveloped field at the present.
On the other hand, as known well, in the simple matrix display, as the number of electrodes increases, crosstalk will cause reduction in contrast and increase in voltage in the case of the passive type, and reduction in brightness and increase in voltage in the case of the active type. To avoid such decline of display characteristics, development of a display panel called "active matrix type" has been lately activated. In the active matrix display panel, different from the panel structure in FIG. 15, one or a plurality of nonlinear resistance elements, thin film transistors or other switching elements are provided for each pixel electrode. As a result, lower voltage and higher brightness by prevention of crosstalk or extension of voltage application time can be achieved, and a high quality display can be realized even if the number of pixels is increased. The conventional manufacturing method of active matrix type display substrate is, for instance, for liquid crystals, as shown on pages 113 to 119 of The Latest Technology of Liquid Crystal by Shoichi Matsumoto et al. (first published 1983 by Kogyo Chosa Kai), a manufacturing method using the film forming a photo etching technology, and it is necessary to put and pull the substrate in and out of the vacuum environment many times when forming electrode films and semiconductor films. When patterning these films provided nearly on the entire surface into a required shape, it is required to repeat many times the photo etching process of applying the photosensitive resist and etching by mask exposure, which raises serious problems in the process cost and yield. Disregarding the cost and yield, from a different point of view, the existing semiconductor manufacturing facility may be used to produce up to A4 size panels, but when a single meter-wide display panel is desired, nothing has been completely developed as for the film uniform depositing apparatus and fine photo etching facilities (resist coater, large size photo mask making machine, uniform exposure unit, etc.).
Alternatively, a method of making active matrix substrate without using the photo etching process is known, for example, on pages 39 to 55 of "Large Scale Integration for Display Screen" Proc. of the SID, Vol. 17/1, 1976, or pages 140 to 150 of "Large Area Masking Techniques for Thin Film Transistor Arrays" SPIE Vol. 100, 1977. Here it is also attempted to make up an active matrix substrate without breaking the vacuum environment at all, by putting the substrate into an evaporating machine and replacing the deposition mask according to the sediment, or moving the deposition mask having a specified hole shape to a specified position on the stationary substrate surface by computer control and evaporating the electrode, insulation layer or semiconductor layer every time. This method does not require the photo etching process, and is excellent in that an active matrix substrate is made up by one pump down, but to form a delicate pattern it is necessary to cause the delicately processed deposition mask tightly on the substrate, and it is attempted to use a magnetic mask and achieve tight contact with the substrate by means of the magnet provided on the back of the substrate.
Hence, making of a large meter-wide substrate involves
(1) Difficulty in causing the deposition mask to contact the substrate uniformly and two-dimensionally; PA1 (2) Difficulty in making high precision, faultless two-dimensional large deposition mask PA1 (4) Complicatedness in control of replacing the deposition mask many times in the vacuum environment and forming patterned film of specified shape by gradually forming the film by setting the position of one deposition mask many times, as well as delay in manufacturing speed, thereby failing to be a manufacturing method of large size active matrix substrate suited to mass production from the the viewpoint of either facility and manufacturing processes.
(3) Difficulty in forming a uniform thickness film on a two-dimensional large area having; and
Hence, at present, manufacturing method of display substrate for displaying character or graphic information of large meter size and high quality has not been developed yet, both for the simple matrix and the active matrix.